Non-uniformly perforated plastic bag

ABSTRACT

Provided is a perforated plastic bag wherein the volume of said bag is 100 liters or more; wherein the average perforation diameter is 500 micrometers or less; wherein said plastic bag comprises a lower zone and a top zone, wherein the perforation density of said lower zone is greater than the perforation density of said top zone. Also provided is a method of using such a plastic bag.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is a divisional of U.S. application Ser. No.14/437,371, filed Apr. 21, 2015, which is a national stage entry under35 USC §371(b) of PCT International Application No. PCT/US2013/065614,filed Oct. 18, 2013, and claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application Ser. No. 61/718,320, entitled “NONUNIFORMLYPERFORATED PLASTIC BAG,” which was filed on Oct. 25, 2012, the entiretyof each of which is hereby incorporated herein by reference.

Bananas are normally harvested by cutting a bunch of bananas from thepseudostem on which it grew. Subsequent to harvest, bunches are oftenbroken down into smaller connected groups called “hands” or,synonymously, “clusters”. It is common to harvest and then ship bananaswhile the peels are green. Long-distance shipment is often performed atlow temperature (for example, at 14° C.). Bananas are considered toripen very slowly during such shipment, during which the bananasnormally remain green.

Bananas, during shipment, are often packed in relatively large boxesthat hold 5 kg or more of bananas. One commonly used size box holdsapproximately 18 to 19 kg. A typical packing process begins by insertinga kraft paper liner into the box. The kraft paper liner is typicallymacro perforated with holes of 0.5 cm to 1.5 cm diameter to provideventilation. In normal industry practice, a plastic liner is theninserted into the box on top of the kraft liner. This plastic liner issometimes an open tube and is sometimes a tube with a sealed bottom. Afirst portion of bananas is then placed into the box. The plastic lineris then folded shut towards the middle of the box, and the shorter endof the kraft paper liner is folded shut towards the middle of the box.Thus, there is a layer of material that resides above the first portionof bananas, and that layer contains both bag material and kraft paper.Then, a second portion of bananas is normally placed into the bag abovethat layer. The plastic liner is normally then pulled closed above thesecond portion of bananas; twisted shut; and then held closed using anappropriate closure device. Often, when the plastic bag is a ModifiedAtmosphere Package (“MAP”), two different atmospheres develop: oneatmosphere surrounding the first portion of bananas and a differentatmosphere surrounding the second portion of bananas. These differentatmospheres can create differences in the ripening advancement and shelflife of the bananas; such differences are undesirable. In some cases,the oxygen level in the bottom half of the bag drops too low and thebananas become anaerobic, which causes them to be ruined. It is desiredto provide a plastic bag that is capable of reducing such differences ininternal atmospheres in different portions of the bag when produce hasbeen packed in those different portions of the bag and after the bag hasbeen tightly sealed.

It is common, once the bananas have reached a location near where theywill be sold, to place them in an enclosed volume and expose them toexogenous ethylene gas. Typical ethylene exposure is 24-48 hours at14-18° C. in an atmosphere that contains ethylene at concentration of100-1000 microliter per liter (ppm). After the exposure to exogenousethylene, the bananas normally ripen more quickly. As the bananas ripen,the peels gradually turn yellow; the peels remain yellow for some time;then the peels develop a small number of black spots; and eventually thebananas become undesirably over-ripe. Sometimes, the bananas are alsoexposed (either before, during, or after exposure to ethylene) to one ormore additional gaseous compound, such as for example1-methylcyclopropene. It is desired to provide a plastic bag that hasthe correct gas transport properties so that, when a bag containingproduce is exposed to an atmosphere that contains ethylene and/oranother gaseous compound, the concentration of ethylene and/or the othergaseous compound, is within the desired concentration range in both thetop and the bottom of the box.

The following is a statement of the invention.

The first aspect of the present invention is a perforated plastic bagwherein the volume of said bag is 100 liters or more; wherein theaverage perforation diameter is 500 micrometers or less; wherein saidplastic bag comprises a lower zone and a top zone, wherein theperforation density of said lower zone is greater than the perforationdensity of said top zone.

The second aspect of the present invention is a method of treatingproduce comprising: (a) placing a first portion of produce in the bottomof the plastic bag of the first aspect; (b) after step (a), folding saidbag to form a layer of bag material over said first portion of produce;(c) after step (b), placing a second portion of produce in said bagabove said layer of bag material; and (d) after step (c), closing saidbag.

The following is a brief description of the drawings.

FIG. 1 is an end view of a box (BX) containing bananas. There are fourrows of bananas that run the length of the box. K is a kraft paperliner. L is a plastic bag, often referred to as a “liner.” B1 and B2 iseach a row of bananas in the bottom portion of the bag. T1 and T2 iseach a row of bananas in the top portion of the bag. OL is the overlaplength by which one end of the kraft paper liner K overlaps the otherend of the kraft paper liner K. G is a gripper that holds the top of thebag L closed.

FIG. 2 is a top view of one embodiment of a plastic bag L. The bag L isshown flattened. The left side 15 is sealed; the right side 16 issealed, and the bottom 8 is sealed. The top 7 is open. The bag Lconsists of two film layers: the layer visible in FIG. 2 and anidentical layer underneath. There are six lanes of microperforations: 9,10, 11, 12, 13, and 14. The dots shown in FIG. 2 are enlarged forclarity. The number of perforations and the distance between them willvary considerably; the dots shown in lanes 9, 10, 11, 12, 13, and 14 donot represent the exact placement of the microperforations, other thanto show that, in the embodiment shown, the microperforations are presentin relatively straight lanes. Lanes 11 and 12 are considerably shorterthan lanes 9, 10, 12, and 13. Each perforation penetrates both layers ofthe bag L. Linc 17 is an imaginary line that is parallel to the top 7and the bottom 8. The distance from the imaginary line L to the top 7 ofthe bag L is DT. The distance from the imaginary line to the bottom 8 ofthe bag L is DB.

The following is a detailed description of the invention.

As used herein, a bag is a flexible enclosure. A bag has one opening; itis possible to place one or more objects inside the bag and then closethe opening. It is not necessary that the bag be able to support theweight of the object or objects inside it.

A plastic bag is a bag, the composition of which contains 50% or morepolymer by weight based on the weight of the bag.

A “rectangular” bag is a bag for which it is possible to lay the bag ona flat surface and flatten the bag so that it exists as two identicalflat layers, one on top of the other, and the horizontal shape of thosetwo layers is a rectangle. When a rectangular bag is laid down that way,the edge of the opening forms one side of the rectangle; that edge isknown herein as the top of the bag. The edge opposite to the top of thebag is known herein as the bottom of the bag. The “zones” of the bag maybe determined as follows: an imaginary line is considered that isparallel to top of the bag and parallel to the bottom of the bag; arectangle is formed by the imaginary line, the sides of the bag, and thetop of the bag; the portion of the bag encompassed by that rectangle,including both layers of the bag, is known herein as the top zone of thebag. Additional imaginary lines may be considered that are parallel tothe first imaginary line and that are located between the firstimaginary line and the bottom of the bag. The portion of the bagencompassed by the rectangle formed by the imaginary line closest to thebottom of the bag, the sides of the bag, and the bottom of the bag isknown herein as the bottom zone. Each rectangle formed by two imaginarylines and the sides of the bag encompasses an “intermediate” zone. Theintermediate zones (if any) and the bottom zone are known collectivelyas lower zones.

If the bag is not rectangular, the zones are determined as follows. Theopening of the bag is gathered together to close the bag. The bag isthen suspended from the closure and allowed to hang freely. An imaginaryhorizontal plane is considered that is between the closure and thebottom-most point of the bag. The portion of the bag above that plane isthe top zone of the bag. Additional imaginary horizontal planes may beconsidered in between the first imaginary horizontal plan and thebottom-most point of the bag. The intermediate, bottom, and lower zonesare then determined as in the case of the rectangular bag.

As used herein, “banana” refers to any member of the genus Musa,including, for example, bananas and plantains.

As used herein, a “film” is an object made of polymer that is muchsmaller in one dimension (the “thickness”) than in the other twodimensions and that has a relatively uniform thickness. Film hasthickness of 1 mm or less. As used herein, a polymeric film is a film,the composition of which contains 50% or more polymer by weight based onthe weight of the film.

As used herein, a “monomer” is a compound that has one or morecarbon-carbon double bond that is capable of participating in apolymerization reaction (i.e., a chemical reaction among monomers thatforms a polymer). As used herein, an “olefin monomer” is a monomer, themolecules of which contain only atoms of carbon and hydrogen. As usedherein, “polar monomer” is a monomer, the molecules of which contain oneor more polar group.

A “polymer,” as used herein, is a relatively large molecule made up ofrepeated units of the reaction products of monomers. Polymers may havestructures that are linear, branched, star shaped, looped,hyperbranched, crosslinked, or a combination thereof; polymers may havea single type of repeat unit (“homopolymers”) or they may have more thanone type of repeat unit (“copolymers”). Copolymers may have the varioustypes of repeat units arranged randomly, in sequence, in blocks, inother arrangements, or in any mixture or combination thereof.

As used herein, a perforation is a hole that penetrates through a film.The size of a perforation is best described by its open area either inactual units of area such as micrometer or mm² or by a diameter of acircle with the same area. The size of the perforation can be measuredin several ways. One such way is to obtain a digital photograph of theperforation using a microscope at a known magnification such as 50× anda photograph of a calibration tool such as a stage micrometer at thesame magnification. Using a pixel count program such as ImageJ, thecalibration photograph can be used to calibrate the size of anindividual pixel and the ImageJ software can be used to count the numberof pixels within the perforation area. Another more direct method is touse a instrument specifically designed to measure area of small objectssuch as that sold by Keyence Corporation or Micro-Vu. These systemsprovide a best fit ellipse to the perforation as expressed by theelliptical parameters “a” and “b”.

A hole of diameter 500 micrometers or smaller is known herein as amicroperforation. A film having multiple microperforations is knownherein as a microperforated film. A hole of diameter 1 millimeter orlarger is known herein as a macroperforation. A film having multiplemacroperforations is known herein as a macroperforated film.

A film or a portion of a film that has multiple perforations may becharacterized by the perforation density, which is the number ofperforations per unit of surface area of the film.

As used herein, when a ratio is said to be “X:1 or higher,” it is meantthat the ratio is Y:1, where Y is greater than or equal to X. Forexample, if it is stated herein that a ratio is “5:1 or higher,” it ismeant that that ratio may be, for example, 5:1 or 6:1 or 100:1 but maynot be, for example, 4:1 or 0.1:1. Similarly, when a ratio is said to be“W:1 or lower,” it is meant that the ratio is Z:1, where Z is less thanor equal to W. For example, if it is stated herein that a ratio is “20:1or lower,” it is meant that that ratio may be, for example, 20:1 or 19:1or 1:1 but may not be, for example, 21:1 or 90:1.

An enclosure that is designed to contain produce (i.e., fruits orvegetables) in a atmosphere other than normal ambient air is called a“Modified Atmosphere Package” (MAP). Passive MAP takes advantage of thefact that some produce (bananas, for example) respire after harvest.Thus such produce, when placed in an enclosure, among other processes,consumes oxygen and produces carbon dioxide. The MAP can be designed sothat diffusion through the solid exterior surfaces of the MAP andpassage of gas through any perforations that may be present in theexterior surface of the MAP maintain preferred levels of oxygen, carbondioxide, and optionally other gases (such as, for example, water vaporor ethylene or both).

It is useful to characterize the inherent gas transmissioncharacteristics of a polymeric film. By “inherent” it is meant theproperties of the film itself, in the absence of any perforations orother alterations. Industry standard methods ASTM D3985 for O2, ASTM1434 for CO2, and ASTM F1249 for H2O can readily be used to characterizethe gas transmission characteristics of a polymer film.

As used herein a cyclopropene compound is any compound with the formula

where each R¹, R², R³ and R⁴ is independently selected from the groupconsisting of H and substituted and unsubstituted hydrocarbyl groups.

The concentration of a substance in an atmosphere is characterizedherein either as parts of substance by volume per one million parts byvolume of atmosphere (ppm) or as parts of substance by volume per onebillion parts by volume of atmosphere (ppb).

The present invention involves a plastic bag. Preferably, the bag iscapable of behaving as a passive MAP for bananas.

Preferably, the composition of the plastic bag is polymeric film.Preferable polymeric films have average thickness of 5 micrometer ormore; more preferably 10 micrometer or more; more preferably 15micrometer or more. Preferable polymeric films have average thickness of200 micrometer or less; more preferably 100 micrometer or less; morepreferably 50 micrometer or less.

Preferably, the composition of the bag contains, by weight based on theweight of the bag, polymer in the amount of 75% or more; more preferably85% or more; more preferably 90% or more.

Some suitable polymer compositions include, for example, polyolefins,polyvinyls, polystyrenes, polydienes, polysiloxanes, polyamides,vinylidene chloride polymers, vinyl chloride polymers, copolymersthereof, blends thereof, and laminations thereof. Suitable polyolefinsinclude, for example, polyethylenes, polypropylenes, copolymers thereof,blends thereof, and laminations thereof. Suitable polyethylenes include,for example, low density polyethylene, ultralow density polyethylene,linear low density polyethylene, metallocene-catalyzed polyethylene,copolymers of ethylene with polar monomers, medium density polyethylene,high density polyethylene, copolymers thereof and blends thereof.Suitable polypropylenes include, for example, polypropylene and orientedpolypropylene. In some embodiments, low density polyethylene is used. Insome embodiments, copolymer of styrene and butadiene is used.

Preferred polymer compositions contain one or more polyolefin; morepreferred is polyethylene; more preferred is metallocene-catalyzedpolyethylene. More preferred polymer compositions contain one or morepolyolefin and one or more copolymer of an olefin monomer with a polarmonomer. Preferred polar groups are hydroxyl, thiol, carbonyl,carbon-sulfur double bond, carboxyl, sulfonic acid, ester linkages, andcombinations thereof. Suitable copolymers of an olefin monomer with apolar monomer include, for example, such polymers available from DuPontcalled Elvax™ resins. Preferred copolymers are copolymers of ethylenewith one or more polar monomer. Preferred polar monomers are vinylacetate, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid,methacrylic acid, and mixtures thereof; more preferred is vinyl acetate.

Preferred are polymeric films with inherent oxygen permeabilitycoefficient, in units of cm³ _(0C) mil/(m² day), of 2,000 or higher;more preferably 4,000 or higher; more preferably 6,000 or higher.Preferred are polymeric films with inherent oxygen permeabilitycoefficient, in units of cm³ _(0C) mil/(m² day), of 50,000 or lower;more preferably 25,000 or lower; more preferably 15,000 or lower.

Preferred are polymeric films with inherent carbon dioxide permeabilitycoefficient, in units of cm³ _(0C) mil/(m² day), of 10,000 or higher;more preferably 20,000 or higher; more preferably 30,000 or higher.Preferred are polymeric films with inherent carbon dioxide permeabilitycoefficient, in units of cm³ _(0C) mil/(m² day), of 100,000 or lower;more preferably 75,000 or lower; more preferably 60,000 or lower.

Polymeric film is used that has perforations. Preferably, the holes havemean diameter of 5 micrometers or more; more preferably 10 micrometersor more; more preferably 20 micrometers or more; more preferably 50micrometers or more; more preferably 100 micrometers or more.Preferably, the holes have mean diameter 300 micrometers or less; morepreferably 200 micrometers or less.

The perforations may be arranged in straight lines, in multiple straightlines, in random patterns, or in combinations thereof. When perforationsare arranged in one or more straight lines, the spacing betweenperforations may be the same for the entire line or may vary along theline. When perforations are arranged in one or more straight lines, thelines may be located at and/or near the center of the bag, at and/ornear the edge of the bag, or any combination thereof.

Holes in polymeric film may be made by any method. Suitable methodsinclude, for example, laser perforation, hot needles, flame, low-energyelectrical discharge, and high-energy electrical discharge. Onepreferred method is laser perforation. Among embodiments in which laserperforation is used, it is preferred to design or select polymeric filmthat is well suited to laser perforation. That is, the polymeric film isdesigned or selected so that the laser easily makes holes that are roundand have predictable size. Preferred laser is a carbon dioxide laser.For different polymeric film compositions, the appropriate wavelength oflaser light may be chosen. For polymeric films that contain polyethyleneand/or copolymers of ethylene with one or more polar monomer, it ispreferred to choose a carbon dioxide laser producing infrared light thatincludes infrared light of wavelength 10.6 micrometer.

A bag may be made by first making a tube and then sealing one end of thetube to form a bag.

Preferred are rectangular bags.

Preferred are bags (herein called “B40” bags) that have sufficientcapacity to enclose 19 kg of average-sized bananas in a configuration asdepicted in FIG. 1.

It is useful to characterize a zone of a perforated bag by theperforation density, which is the quotient that results when dividingthe total area of all the perforation in that zone by the surface areaof that zone.

Among B40 bags, preferred are bags in which the top zone has perforationdensity, in units of mm² of perforation per m² of the surface area ofthe bag, of 2 or higher; more preferably 4 or higher. Among B40 bags,preferred are bags in which the top zone has perforation density, inunits of mm² of perforation per m² of the surface area of the bag, of 12or lower; more preferably 10 or lower.

Among B40 bags, preferred are bags that have one or more lower zone inwhich the ratio of the perforation density in that lower zone to theperforation density in the top zone is 1.01:1 or greater; morepreferably 1.1:1 or greater; more preferably 1.2:1 or greater. Among B40bags, preferred are bags that have one or more lower zone in which theratio of the perforation density in that lower zone to the perforationdensity in the top zone is 6:1 or lower; more preferably 5:1 or lower.

Among B40 bags, preferred are bags that have exactly two zones. Two-zonebags may be characterized by the ratio (the “division ratio”) of thedistance from the top of the bag to the imaginary line (or plane) thatdivides the zones to the distance from the imaginary line (or plane)that divides the zones to the bottom of the bag. Preferably, thedivision ratio is 1:1 or greater; more preferably 1.5:1 or greater; morepreferably 1.8:1 or greater. Preferably, the division ratio is 3:1 orless; more preferably 2.5:1 or less.

Preferred B40 bags have volume of 200 liter or more; more preferably 300liter or more. Preferred bags have volume of 2,000 liter or less; morepreferably 1,500 liter or less.

Preferred embodiments of the plastic bag of the present invention may bedescribed by reference to FIG. 2. Preferably, the bag L has plural linesof perforation 9, 10, 11, 12, 13, and 14. Lines of perforation 9, 10,13, and 14, extend 90% or more of the length of bag L; the length of bagL is the distance from the top 7 to the bottom 8. The bag L ispreferably made by extruding and blowing a tube in the direction fromthe bottom 8 to the top 7 (or from the top 7 to the bottom 8). Becauseof the extrusion and film-blowing process, the sides 15 and 16 areclosed. Lines of perforation 11 and 12 are shorter than lines 9, 10, 13,and 14. Imaginary line 17 is preferably drawn where lines of perforation11 and 12 end. The ratio of distance DT to distance DB is preferably2.5:1 to 1.5:1.

In preferred embodiments, the plastic bag of the present invention isput to use as follows, as illustrated in FIG. 1.

First, a cardboard box BX is provided that is large enough to hold 19 kgof average-sized bananas. The cardboard box BX has multiple holes ofdiameter 20 mm or larger, to allow ventilation. A kraft paper liner K isinserted into the box; preferably the kraft paper liner K ismacroperforated with holes of 6 mm to 14 mm diameter to provideventilation. A plastic bag of the present invention L is then insertedinto the box on top of the kraft paper liner K. Two rows of bananas (B1and B2) are then placed into the center of the box BX running the lengthof the box BX. The plastic bag L is then folded shut, above the two rowsof bananas B1 and B2, towards the middle of the box BX and the shorterend of the kraft paper liner K is folded shut, above the two rows ofbananas B1 and B2, towards the middle of the box BX. The length of thekraft paper liner K is preferably approximately 90 cm and is preferablyarranged such that there is an overlap OL of the two ends. This overlaphelps prevent scuffing of the top layers of bananas during shipment. Theplastic bag L is then folded open on top of the short end of the kraftpaper liner K. Then, a row of bananas T1 is placed on top of the plasticbag L. The long end of the kraft paper liner K is then folded shut overthe crowns or tips of the top row of bananas T1 and the plastic bag L ispulled open above the long side of the kraft paper liner K. Another rowof bananas T2 is then placed on the top of the plastic bag L on thislong kraft paper liner side. The plastic bag L is pulled closed above T1and T2 twisted shut; and then held closed using a gripping device G.Preferably, G is a rubber band; a tape closure; or some otherappropriate closure device. The closing of the micro-perforated plasticbag L enables a Modified Atmosphere (MA) to develop inside the plasticbag L during the shipment, ripening, and storage of the bananas.

The kraft liner overlap OL provides enough of a barrier to gas movementthat the single closed plastic bag L creates two distinct MA in the box;one MA for the bottom layer of bananas; B1 and B2; and one MA for thetop layer of bananas; T1 and T2.

If a plastic bag of the present invention were not used, these distinctMA's for the bottom and top of the box could create undesirably largedifferences in the ripening advancement and shelf life of the bananas.If a plastic bag of the present invention were not used the gas movementbarrier could also cause the bananas in the bottom of the box to goanaerobic if the oxygen level is too low in the MA of the bottom of thebox, and going anaerobic ruins the bananas.

The length of the kraft paper liner K is defined as the length as shownin FIG. 1. That is, the length of the kraft paper liner K is takenherein to be the distance along the kraft paper liner K from one of theoverlapped ends of the kraft paper liner K, down one side of the box BX,across the bottom of the box BX, up the other side of the box BX, to theother of the overlapped ends of the kraft paper liner K.

The length of the plastic bag L for the bottom of the box BX and the topof the box BX may be different. The length of the bag L for the bottomof the box BX is taken to be the length of an imaginary line drawn alongthe surface of the plastic bag L where it is adjacent to the kraft paperliner K as shown in FIG. 1. Preferably, ratio of the length of theplastic bag L for the bottom of the box BX to the length of the kraftpaper liner K is 0.5:1 or higher; more preferably 0.75:1 or higher; morepreferably 0.9:1 or higher. Preferably, ratio of the length of theplastic bag L for the bottom of the box BX to the length of the kraftpaper liner K is 2:1 or lower; more preferably 1.3:1 or lower; morepreferably 1.1:1 or lower.

Preferably, a plastic bag L is used as illustrated in FIG. 2 in such away that the length of the plastic bag L for the bottom of the box BX is2*DB.

It is useful to consider the portion of the plastic bag L that enclosesbanana rows T1 and T2; that portion is known herein as the “topenclosure” of plastic bag L. For example, in FIG. 1, the top enclosureof plastic bag L is the portion of plastic bag L that surrounds bananarows T1 and T2. The top enclosure is that portion of plastic bag Lbetween the part of the plastic bag L that is closed by gripper G andthe part of the plastic bag L that participates in the fold that liesabove banana rows B1 and B2 and below banana rows T1 and T2.

It is also useful to consider the portion of the plastic bag L thatencloses banana rows B1 and B2; that portion is known herein as the“bottom enclosure” of plastic bag L. For example, in FIG. 1, the bottomenclosure of plastic bag L is the portion of plastic bag L thatsurrounds banana rows B1 and B2. The bottom enclosure is that portion ofplastic bag L between the bottom 8 of the plastic bag L and the part ofthe plastic bag L that participates in the fold that lies above bananarows B1 and B2 and below banana rows T1 and T2.

The surface area of the top enclosure of plastic bag L is known hereinas ATOP. The surface area of the bottom enclosure of plastic bag L isknown herein as ABOT. Preferably, ratio of ATOP to ABOT is 3:1 or lower;more preferably 2.5:1 or lower. Preferably, ratio of ATOP to ABOT is 1:1or higher; more preferably 1.2:1 or higher.

Preferably, the ratio of the weight of bananas enclosed in the topenclosure of plastic bag L to the weight of bananas enclosed in thebottom enclosure of plastic bag L (i.e., the ratio of the weight of T1plus T2 to the weight of B1 plus B2) is 0.6:1 or higher; more preferably0.8:1 or higher. Preferably, the ratio of the weight of bananas enclosedin the top enclosure of plastic bag L to the weight of bananas enclosedin the bottom enclosure of plastic bag L is 3:1 or lower; morepreferably 2:1 or lower; more preferably 1.5:1 or lower.

Preferably, the portion of the plastic bag L shown in FIG. 1 enclosingbanana rows B1 and B2 is the bottom zone of the plastic bag L. That is,preferably the portion of the bag L shown in FIG. 2 between the bottom 8and the line 17 drawn at the tops of the short lines of perforation 11and 12 forms the bottom enclosure of the plastic bag L. Preferably theportion of the plastic bag L shown in FIG. 1 enclosing banana rows T1and T2 is the top zone of the plastic bag L. That is, preferably theportion of the bag L shown in FIG. 2 between the top 7 and the line 17drawn at the tops of the short lines of perforation 11 and 12 forms thetop enclosure of the plastic bag L, while a small portion of the plasticbag L near the top 7 is envisioned to be gathered together under closingdevice G.

Preferably, the kraft paper liner K is perforated. Preferably,perforations in the kraft paper liner K are located both on the portionof the kraft paper liner K that is on the bottom of the box BX on theportion of the kraft paper liner K that is positioned between the bottomrow of bananas B2 and the top row of bananas T2 as well as on theportion of the kraft paper liner K that is positioned between the bottomrow of bananas B1 and the top row of bananas T1.

Preferably, the perforations in the kraft paper liner have averagediameter of 0.5 cm or higher; more preferably 1 cm or higher.Preferably, the perforations in the kraft paper liner have averagediameter of 30 cm or smaller; more preferably 10 cm or smaller; morepreferably 3 cm or smaller.

The sum of the number of holes in the kraft paper liner K located on theportion of the kraft paper liner K that is positioned between the bottomrow of bananas B2 and the top row of bananas T2 plus the number of holesin the kraft paper liner K located on the portion of the kraft paperliner K that is positioned between the bottom row of bananas B1 and thetop row of bananas T1 is known herein as “NSIDES.” Preferably, NSIDES is10 or higher; more preferred is 20 or higher; more preferred is 35 orhigher. Preferably, NSIDES is 600 or lower; more preferred is 500 orlower.

It is believed that reducing the length of the kraft paper liner; addingextra ventilation holes to the kraft paper liner; or adding circularnotches to the edge of the kraft paper liner can also help equalize thegas environment between the bottom and top of the box BX by reducing thegas flow restriction or creating a “chimney” between bottom and toplayers of bananas.

FIG. 1 depicts a preferred embodiment, and other embodiments are alsoenvisioned. For example, the use of produce other than bananas isenvisioned. Preferably the produce is chosen from fruits and vegetables.Produce may be climacteric or non-climacteric. Among non-climactericproduce, preferred are asparagus, broccoli, brussels sprouts, okra,leafy greens, fresh peas, and sweet corn. Climacteric produce ispreferred. Preferred climacteric produce is banana, avocado, and melon;more preferred is banana.

Also, embodiments are envisioned in which kraft paper liner K is notused. Also envisioned are embodiments in which a box BX is not used.Envisioned are embodiments that use produce other than bananas. Further,embodiments are envisioned in which produce is arranged differently fromthe arrangement shown in FIG. 1. Preferred are arrangements of producein which there are at least two layers of produce, with some portion ofthe plastic bag L residing in between the layers of produce.

Also envisioned are embodiments (herein called “non-fold” embodiments)in which kraft paper liner K is not used and in which the plastic bag Lis not folded. In non-fold embodiments, there is no layer of bagmaterial between distinct layers of produce. In non-fold embodiments, arelatively large proportion of the surface area of the bottom portion ofthe plastic bag L may be in contact with the sides and/or bottom of thebox BX in comparison with the top portion of the plastic bag L; thus,contact of the box BX with the bottom portion of the plastic bag L mayrestrict gas transport in and out of the plastic bag L more than doescontact of the box BX with the top portion of plastic bag L. Thereforeit is contemplated that the plastic bag L will provide benefits innon-fold embodiments. Non-fold embodiments are contemplated for use withproduce other than bananas.

Preferred are embodiments in which the total amount of bananas insidethe plastic bag of the present invention is 4 kg or more; morepreferably 10 kg or more; more preferably 15 kg or more. Preferred areembodiments in which the total amount of bananas inside the plastic bagof the present invention is 30 kg or less; more preferably 25 kg orless; more preferably 22 kg or less.

It is useful to characterize a portion of a plastic bag of the presentinvention that contain bananas by the banana-specific perforation, whichis defined as the total area of the holes in that portion of the bag(for example, in units of square millimeters) divided by the mass of thebananas (for example, in units of kilograms) enclosed by that portion ofthe plastic bag.

The preferred banana-specific perforation of the top enclosure of aplastic bag of the present invention that contain bananas is 0.025mm²/kg or more; more preferably 0.05 mm²/kg or more; more preferably0.075 mm²/kg or more. The preferred banana-specific perforation of thetop enclosure of a plastic bag of the present invention that containbananas is 3 mm²/kg or less; more preferably 2.5 mm²/kg or less; morepreferably 2 mm²/kg or less.

Preferably, for a plastic bag of the present invention that containsbananas, the ratio of the banana-specific perforation of the bottomenclosure to the banana-specific perforation of the top enclosure is 6:1or less; more preferably 5:1 or less; more preferably 4:1 or less.Preferably, for a plastic bag of the present invention that containsbananas, the ratio of the banana-specific perforation of the bottomenclosure to the banana-specific perforation of the top enclosure is0.3:1 or higher; more preferably 0.4:1 or higher; more preferably 0.6:1or higher.

In some embodiments, bananas are harvested and immediately placed intobags of the present invention. In preferred embodiments, the time fromharvest to placement into bags of the present invention is 14 days orless, more preferably 7 days or less, more preferably 2 days or less. Inpreferred embodiments, harvested bananas are placed into bags of thepresent invention prior to shipment, and the harvested bananas remain inthe bags of the present invention during shipment. In some embodiments,bananas are shipped to a destination that is near the intended point ofsale to consumers. As used herein, “near the intended point of sale toconsumers” means a location from which it is capable to transport thebananas to the point of sale to consumers in 5 days or fewer by truck orother surface transportation.

In some embodiments, at the time of packing, air can be sucked out fromthe void areas using a hand held vacuum pump and then quickly sealed toaid in passive MAP development. Alternatively, in some embodiments, bagscan also be subject to predefined atmosphere composition also known asactive MAP or held under controlled atmosphere (CA) conditions for longterm transit and storage. The commonly used atmospheres for active MAPor CA are 3-5% O₂ and 3-5% CO₂, by weight based on the weight of theatmosphere.

A few useful categories of produce may be defined. As defined herein,“chilling-sensitive” produce is produce that loses desirable qualitiesif it is exposed to long periods of temperatures at or below 12° C. Forexample, bananas and some other tropical produce are chilling-sensitive.As defined herein, “EE” produce is produce that does not ripen desirablyuntil exposed to exogenous ethylene. For example, green bananas as theyare normally harvested are EE produce. As defined herein, “HT” produceis produce that does not ripen desirably as long at it is stored below10° C. and then does ripen normally after exposure to higher temperatureof 20° C. or higher. For example, avocado and mango are HT produce.

Preferably, plastic bags of the present invention that contain produceare stored for relatively long periods of time, preferably at reducedtemperature. Such storage may take place, for example, during shipmentof produce from one location to another. Preferably, plastic bags of thepresent invention that contain produce are stored for 7 days or more;more preferably 10 days or more. Preferably, plastic bags of the presentinvention that contain produce are stored for 20 days or fewer.Preferably, plastic bags of the present invention that containchilling-sensitive produce are stored at temperature of 13° C. orhigher. Preferably, plastic bags of the present invention that containproduce are stored at temperature of 20° C. or lower; more preferably15° C. or lower.

Preferably, plastic bags of the present invention that contain EEproduce are exposed to an atmosphere that contains ethylene. Thepreferred temperature for performing exposure to ethylene is 13.5° C. orhigher; more preferably 14° C. or higher. The preferred temperature forperforming exposure to ethylene is 18.3° C. or lower.

In preferred methods of exposing plastic bags of the present inventionthat contain EE produce to ethylene, bags of the present invention thatcontain produce are exposed to an atmosphere that contains molecules ofethylene. The preferred concentration of ethylene in the atmosphere is20 ppm or higher; more preferably 50 ppm or higher; more preferably 100ppm or higher. The preferred concentration of ethylene in the atmosphereis 1,000 ppm or less; or 500 ppm or less; or 300 ppm or less.

The preferred duration of the exposure of plastic bags of the presentinvention that contain EE produce to an atmosphere that containsethylene is 8 hours or more; more preferably 16 hours or more; morepreferably 20 hours or more. The preferred duration of the exposure ofplastic bags of the present invention that contain EE produce to anatmosphere that contains ethylene is 48 hours or less; more preferably36 hours or less; more preferably 24 hours or less.

Among embodiments in which HT produce is used, it is preferred tomaintain the produce below 15° C. until immediately prior todistribution to retail stores, at which time the produce is preferablykept at 20 to 22° C. for 24 to 48 hours.

Preferably, plastic bags of the present invention that contain produceare exposed to one or more cyclopropene compound. In preferredcyclopropene compounds, R², R³ and R⁴ are hydrogen. Preferably, R¹ is asubstituted or unsubstituted C1-C8 alkyl group; more preferably, R¹ ismethyl. Preferably, bags of the present invention that contain produceare exposed to an atmosphere that contains molecules, in gaseous form,of one or more cyclopropene compound. Preferably, the concentration ofcyclopropene compound is 0.5 ppb or higher; more preferably is 1 ppb orhigher; more preferably is 10 ppb or higher; more preferably 100 ppb orhigher. Preferably, the concentration of cyclopropene compound is 100ppm or lower, more preferably 50 ppm or lower, more preferably 10 ppm orlower, more preferably 5 ppm or lower.

The preferred temperature for performing exposure to cyclopropenecompound is 8° C. or higher; more preferably 11° C. or higher. Thepreferred temperature for performing exposure to cyclopropene compoundis 18.3° C. or lower.

The preferred duration of the exposure of plastic bags of the presentinvention that contain produce to an atmosphere that containscyclopropene compound is 4 hours or more; more preferably 8 hours ormore; more preferably 10 hours or more. The preferred duration of theexposure of plastic bags of the present invention that contain produceto an atmosphere that contains cyclopropene compound is 24 hours orless; more preferably 18 hours or less.

Preferably, plastic bags of the present invention that contain bananasare exposed to an atmosphere containing a cyclopropene compound when thebananas have peel color rating of 2.5 to 3.5 on the 7-stage scale. The7-stage scale is described as follows:

The color of banana peels is rated according to a seven stage ratingscale: stage 1 (dark green); stage 2 (all light green); stage 3 (halfgreen and half yellow); stage 4 (more yellow than green); stage 5 (greentips and necks); stage 6 (all yellow; maybe light green necks, no greentips); stage 7 (yellow flecked with brown). Consumers generally preferto eat bananas in stage 5 or stage 6.

The following are examples of the present invention.

Oxygen concentration was measured using a Pac Check™ 325 (Mocon, Inc.)or equivalent instrument.

Carbon dioxide concentration was measured using a Pac Check™ 325 (Mocon,Inc.) or equivalent instrument.

Perforation diameter was measured using a visual instrument fromMicro-Vu Corporation, using best fit elliptical axes and thencalculating the area of the ellipse and then calculating the diameter ofa circle having the same diameter.

The following abbreviations are used:

P′O2=Oxygen Permeability Coefficient in units of cm³ _(0C) mil/(m² day)

P′CO2=Carbon Dioxide Permeability Coefficient in units of cm³ _(0C)mil/(m² day)

Bottom=bottom 45.7 cm (18 inches) of the bag

Top=top 91.4 cm (36 inches) of the bag

PE=ELITE™ 5400G enhanced polyethylene resin (Dow Chemical Co.)

EVA=EB502AA ethylene/vinyl acetate copolymer (Westlake Chemical Co.)

Slip=Ampacet 101797

Anti-Block=Ampacet 10063

P-Area=total area of perforations, in mm2

S-Area=surface area of that portion of the bag, in m2

P-Density=P-Area divided by S-Area, in mm2 per m2

P-Ratio=P-Density of the bottom to the P-Density of the top

Av=Average

COMPARATIVE EXAMPLE C1 TO C4: SINGLE CHAMBER BAG IN-COUNTRY PACKAGING

A mono layer film for Comparative Example C1 and Comparative Example C2was produced by extruding a 94 cm (37 inch) diameter tube on aconventional upward blown film line. A mono layer film for ComparativeExample C3 and Comparative Example C4 was produced by extruding a 99.7cm (39.25 inch) diameter tube on a conventional upward blown film line.The composition of the film and the film properties are provided inTables 1A and 1B. The tube film was sealed and scored for tear off onthe film line to produce bags on a roll. The tube film was perforatedusing a beam compression laser perforation system as follows and asdetailed in Table 2A.

In Comparative Examples C1 to C4, each bag had four lines ofperforations similar to lines 9, 10, 13, and 14 in FIG. 2. Every line ofperforation ran the length of the bag; there was no abbreviated line ofperforations similar to lines 11 and 12 in FIG. 2. In ComparativeExamples C1 and C2, the distances from the left side of the bag to eachline of perforation was as follows: 3.8 cm, 45.7 cm, 83.8 cm, and 89.9cm. In Comparative Examples C3 and C4, the distances from the left sideof the bag to each line of perforation was as follows: 4.1 cm, 50.5 cm,92.1 cm, and 96.4 cm.

The perforation area is in units of mm²; for the bottom 45.7 cm (18inch) length of the bag and for the top 91.4 cm (36 inch) length of thebag is given in Table 2B.

The perforated bags were used to package bananas in Guatemala in theconventional manner as shown in FIG. 1 and shipped to the United Statesfor ripening. The bananas were ripened as follows. The temperaturesshown are pulp temperatures; if necessary, the thermostat was lowered sothat pulp temperature remained at the desired temperature despite anyrespiration that may be taking place in the bananas.

day 0: 17.8° C. (64° F.), in normal air

day 1: 17.8° C. (64° F.), ethylene at 200 ppm for 24 hours

day 2: 17.8° C. (64° F.), room was vented for 30 min., then re-sealed.

day 3: 17.8° C. (58° F.)

day 4: 14.4° C. (58° F.)

day 5: 14.4° C. (58° F.)

While still in the bags, the bananas were then treated with1-methylcyclopropene (1-MCP) on Day 5 as follows. The bags with thebananas inside were place in an enclosed volume, at 13.3° C. (56° F.),and sufficient 1-MCP was released into that volume to give aconcentration of 1000 ppb. The volume remained enclosed and was held at13.3° C. for 12 hours. The bananas were then removed from the ripeningroom and stored at 21.7° C. (71° F.). The gas atmosphere in the bottomand top portion of the bag was measured on Day 2, Day 3, and Day 4 post1-MCP treatment with the results given in Table 3.

The desired oxygen concentration in the atmosphere of the bag was 5.5%to 11.5% by weight. The oxygen concentration in the bottom of the bagfor Comparative Examples C1 to C4 was unacceptably low. Also,Comparative Examples C3 and C4 had anaerobic characteristics present inthe banana taste.

TABLE 1A Film Composition Anti- Tube Width Thickness Example PE EVA SlipBlock cm (inch) micrometer (mil) C1 69% 20% 6% 5% 91.4 (36) 26.9 (1.06)C2 79% 12% 4% 5% 91.4 (36) 26.4 (1.04) C3 79% 12% 4% 5% 99.1 (39) 27.9(1.10) C4 71% 20% 4% 5% 99.1 (39) 26.9 (1.06)Amounts shown are by weight based on the weight of the film.

TABLE 1B Film Properties Tensile Toughness MD Example P'O2 P'CO2 MPa(psi) C1 7,640 40,900 61.81 (8965) C2 9,100 45,400 56.95 (8260) C3 8,82044,600 59.92 (8690) C4 7,890 41,400 58.12 (8430)

TABLE 2A Film Perforation Details Diameter of perforations, ExampleSpacing of perforations, mm micrometers C1 5.43 114.0 C2 5.44 117.8 C35.49 109.1 C4 5.48 101.5

TABLE 2B Further Film Perforation Details Bottom Top P- S- P- P- S- P-P- Example Area Area Density Area Area Density Ratio C1 6.88 0.836 8.213.75 1.67 8.2 1.00:1 C2 7.33 0.836 8.8 14.66 1.67 8.8 1.00:1 C3 6.230.906 6.9 12.46 1.81 6.9 1.00:1 C4 5.40 0.906 6.0 10.80 1.81 6.0 1.00:1

TABLE 3 Gas Atmosphere Data for Comparative Examples 1 to 4. AverageAverage Average Average Oxygen Oxygen Minimum Carbon Carbon Conc. onConc. on Oxygen Dioxide Dioxide Day 2, Day 2, Conc. Conc. on Conc. onExam- 3, & 4; 3, & 4; Bottom Day 2, 3, & Day 2, ple Bottom Top and Day4; Bottom 3, & 4; Top C1 5.3% 9.2% 4.9% 15.3% 9.7% Day 4 C2 5.1% 8.8%4.3% 15.0% 10.3% Day 4 C3 2.1% 8.0% 2.2% 22.9% 12.0% Day 3 C4 2.4% 7.6%2.4% 22.6% 12.4% Day 3

INVENTION EXAMPLES 1 TO 4

Dual Chamber Bag in Country Packaging

A mono layer film for Invention Examples 1 through Invention Example 4was produced by extruding a 99.7 cm (39.25 inch) diameter tube on aconventional film line. The composition of the film and the filmproperties are provided in Table 4A and 4B. The tube film was sealed andscored for tear off on the film line to produce bags on a roll. The tubefilm was perforated using a beam compression laser perforation system inthe pattern shown in FIG. 2 and as detailed in Table 5A and 5B.Distances were as follows:

from to distance (cm) left side 15 of bag L line 9 7.37 left side 15 ofbag L line 10 12.45 right side 16 of bag L line 14 6.35 right side 16 ofbag L line 13 11.68 right side 16 of bag L line 12 33.27 right side 16of bag L line 11 66.55

The perforation area is in units of mm²; for the bottom 45.7 cm (18inches) length of the bag and for the top 91.4 cm (36 inches) length ofthe bag is given in Table 5. The short lanes of perforations at thebottom of the bag were indexed using an eyespot on the bag and aneyespot reader on the perforation machine. The perforated bags were usedto package bananas in Guatemala in the conventional manner as shown inFIG. 1 and shipped to the United States for ripening. The bananas wereripened using a conventional 5 day ripening cycle as above and thentreated with 1000 ppb of 1-MCP as above on Day 5. The bananas were thenremoved from the ripening room and stored at 21.7° C. (71° F.). The gasatmosphere in the bottom and top portion of the bag was measured on Day2, Day 3, and Day 4 post 1-MCP treatment with the results given in Table6.

The oxygen concentration for the bottom 45.7 cm (18 inches) of thebanana bag is above the desired target of 5.5% or higher while theoxygen concentration in the top 91.4 cm (36 inches) of the banana bag iswithin the target of 11.5% or lower.

TABLE 4A Film Composition for Invention Examples 1 to 4 Anti- Thickness;Example PE EVA Slip Block PPA micrometer (mil) 1 69% 20% 4% 5% 2% 27.4(1.08) 2 69% 20% 4% 5% 2% 27.4 (1.08) 3 69% 20% 4% 5% 2% 27.4 (1.08) 469% 20% 4% 5% 2% 27.4 (1.08)

TABLE 4B Film Properties for Invention Examples 1 to 4 TensileToughness; MD Example P'O2 P'CO2 MPa (psi) 1 7,920 45,700 52.06 (7,550)2 7,920 45,700 52.06 (7,550) 3 7,920 45,700 52.06 (7,550) 4 7,920 45,70052.06 (7,550)

TABLE 5A Film Perforation Details for Invention Examples 1 to 4 FullLane Short Lane Full Lane Perforation Short Lane Perforation PerforationDiameter; Perforation Diameter; Example Spacing; mm micrometer Spacing;mm micrometer 1 5.418 110.2 4.81 116.9 2 5.439 110.2 3.857 116.9 3 5.424110.2 2.686 116.9 4 6.040 110.2 3.392 114.8

TABLE 5B Further Film Perforation Details for Invention Examples 1 to 4Bottom Top P- S- P- P- S- P- P- Example Area Area Density Area AreaDensity Ratio 1 10.48 0.906 11.6 12.88 1.81 7.1 1.6:1 2 11.44 0.906 12.612.83 1.81 7.1 1.8:1 3 13.71 0.906 15.1 12.86 1.81 7.1 2.1:1 4 11.290.906 12.5 11.55 1.81 6.4 2.0:1

TABLE 6 Gas Atmosphere Data for Invention Examples 1 to 4. Av Oxygen AvOxygen Av Carbon Av Carbon Conc. Day Conc. Day Dioxide Conc. DioxideConc. Exam- 2, 3, & 4; 2, 3, & 4; Day 2, 3, & Day 2, 3, & 4; ple BottomTop 4; Bottom Top 1 5.8% 11.0% 14.7% 9.1% 2 6.4% 11.2% 14.5% 8.7% 3 5.7%10.2% 15.0% 12.6% 4 6.3% 9.1% 14.6% 10.5%

What is claimed is:
 1. A method of treating produce comprising (a)placing a first portion of produce in a bottom a plastic bag; (b) afterstep (a), folding said bag to form a layer of bag material over saidfirst portion of produce; (c) after step (b), placing a second portionof produce in said bag above said layer of bag material; and (d) afterstep (c), closing said bag, wherein the plastic bag has a volume of 100liters or more; wherein the plastic bag comprises a plurality ofperforations each having an average perforation diameter of 500micrometers or less; wherein the plastic bag comprises a lower zone anda top zone, and wherein the lower zone has a perforation density that isgreater than a perforation density of perforation density of the topzone.
 2. The method of claim 1, wherein the ratio of said perforationdensity of said lower zone to said perforation density of said top zoneis 1.1:1 or higher.
 3. The method of claim 1, wherein the perforationdensity of the top zone of the plastic bag is 2 mm² of perforation perm² of a surface area of the bag or higher.
 4. The method of claim 1,wherein said produce comprises bananas.
 5. The method of claim 4,wherein the ratio of the banana-specific perforation of the bottomenclosure of said bag to the banana-specific perforation of the topenclosure of said bag is from 0.3:1 to 5:1.
 6. The method of claim 1,further comprising the step of (e) after step (d), storing said bag for7 days or more at 20° C. or lower.
 7. The method claim 6, furthercomprising the step of (f) after step (e), exposing said bag to anatmosphere that contains ethylene.
 8. The method claim 7, furthercomprising the step of (g) after step (f), exposing said bag to anatmosphere that contains a cyclopropene compound.
 9. The method of claim8, wherein the step (g) is performed at a temperature of 8° C. orhigher.
 10. The method of claim 8, wherein step (g) is performed at atemperature of 18.3° C. or lower.
 11. The method of claim 8, whereinstep (g) is performed for 4 hours or more.
 12. The method of claim 8,wherein step (g) is performed for 24 hours or less.
 13. The method ofclaim 7, wherein the concentration of ethylene in the atmosphere is 20ppm or higher.
 14. The method of claim 7, wherein the concentration ofethylene in the atmosphere is 1,000 ppm or less.
 15. The method of claim7, wherein the bag is exposed to the atmosphere that contains ethylenefor 48 hours or less.
 16. The method of claim 1, further comprisingplacing the plastic bag in a box.
 17. The method of claim 16, furthercomprising placing a kraft paper liner in the box prior to placing theplastic bag in the box.
 18. The method of claim 17, wherein the kraftpaper liner comprises perforations.
 19. The method of claim 1, whereinthe first portion of produce and the second portion produce have acombined weight of 4 kg or more.
 20. The method of claim 19, wherein thecombined weight of the first portion of produce and the second portionof produce is 30 kg or less.